Process for the preparation of alkyl, perfluoroalkyl and aryl iodides

ABSTRACT

High yields of alkyl, perfluoroalkyl and aryl iodides are prepared directly from their corresponding carboxylic acids by reaction in solution with iodine and aroyl peroxide or tbutylperoxyisopropyl carbonate. The reaction is conducted at a temperature of about 110*-125* C. for about 2 to 3 hours in solvents such as 1,3-dichloropropane, 1,3-dibromopropane and 1,1,2,2-tetrachlorodifluorethane. Solvents such as 1,2dichloroethane and carbon tetrachloride can be used as solvents but they require longer reaction times.

United States Patent Silbert [54] PROCESS FOR THE PREPARATION OF ALKYL, PERFLUOROALKYL AND ARYL IODIDES [72] Inventor: Leonard S. Siibert, Philadelphia, Pa.

[73] Assignee: The United States of America as represented by the Secretary of Agriculture Mar. 23, 1970 21 Appl. No; 24,924

[22] Filed:

Related US. Application Data [62] Division of Ser. No. 708,804, Feb. 28, 1968, Pat. No.

[52] 11.5. C1 ..260/653 [51] Int. Cl ..C07c 19/08 [58] Field of Search ..260/653 [451 May 30, 1972 [56] References Cited UNITED STATES PATENTS 2,554,219 5/1951 Simons et al ..260/653 3,531,535 9/1970 Silbert ..260/653 FOREIGN PATENTS OR APPLICATIONS 757,893 9/1956 Great Britain ..260/653 Primary ExaminerDaniel D. Horwitz AttorneyR. Hoffman and W. Bier [5 7] ABSTRACT 2 Claims, No Drawings PROCESS FOR THE PREPARATION OF ALKYL, PERFLUOROALKYL AND ARYL IODIDES This application is a division of Ser. No. 708,804, filed Feb. 28, 1968, now U.S. Pat. No. 3,531,535.

A non-exclusive, irrevocable, royalty-free license in the invention herein described, throughout the world for all purposes of the United States Government, with the power to grant sublicenses for such purposes, is hereby granted to the Government of the United States of America.

This invention relates to alkyl, perfluoroalkyl,and aryl iodides and more specificallyto a novel process for preparing these compounds directly from their corresponding carboxylic acids by reaction in solution with iodine and aroyl peroxide or t-butyl perester.

Organic iodides such as cetyl trimethyl ammonium iodide and cetyl pyridinium iodide that can be prepared by the method of this invention find use as disinfectants and germicides. Others, such as cetyl iodide react with tertiary amines to form tetraalkyl ammonium iodide salts which are used as supporting electrolytes in polarography. lodides are also used as dyes such as erythrosin and Rose Bengal, as photographic sensitizers such as the cyanine dyes and in compounds of medical interest such as thyroxin and iodoform. The iodides also find use as intermediates in the preparation of other compounds. Nucleophilic displacement reactions of the iodides yield other compounds such as sulfonic acid esters, nitro derivatives and mercaptans.

As described in copending application entitled Process for the Preparation of Alkyl and Aryl iodides," Ser. No. 708,800, filed Feb. 28, 1968, now abandoned aryl and alkyl iodides can be prepared by decomposition of aroyl and acyl peroxides in selected solvent systems. Practical application of that process requires solvents which are relatively inert to the reactants yet dissolve them without difficulty and solvents which have convenient boiling points, preferably between 90 and 130 C., so that the peroxide decomposes rapidly and controllably.

While investigating other aspects of that reaction, I unexpectedly discovered a new reaction for preparing alkyl, perfluoroalkyl, and aryl iodides. In this reaction, peroxide abstracts hydrogen from the carboxylic acid function and the acyl,perfluoroacyl,or aroyl hypoiodite that is generated decomposes to alkyl,perfluoroalkyl, or aryl iodide, respectively, in accordance with equation 1 illustrated for bensoyl peroxide and an aliphatic acid.

2RI co 1 perfluoro aromatic.

The reaction is conducted in solvents like 1,3- dichloropropane, l,1,2,Z-tetrachlorodifluorethane (Freon l 12) and 1,2-dibromopropane using stoichiometric quantities of acid, peroxide and iodine, i.e., 2 moles of monobasic acid, 1 mole of aroyl peroxide or 2 moles of BPIC, and 1 mole of iodine. However, yields are improved by using higher ratios of iodine. The reactions are depicted by equation 2 for aroyl peroxides and equation 3 for BPIC.

Theoretically, the isopropoxy radical should also abstract hydrogen, but this radical being of lower stability than the tbutoxy radical rapidly decomposes at temperatures above room temperature thereby eliminating the isopropoxy radical in the hydrogen abstraction process. Hence the t-butoxy radical serves to remove the hydrogen atom of the carboxyl group.

When aliphatic acids are reacted with either aroyl peroxide or BPIC, high yields, -90 percent, of alkyl iodides are obtained. High yields are also obtained when aromatic acids are reacted with BPIC.

Carbon tetrachloride and 1,2-dichloroethane can be used as solvents for the reactions but their lower boiling points require longer times to complete the reaction.

Results for conversions of stoichiometric molar ratios of octanoic acid and benzoyl peroxide are recorded in Table I. Iodobenzene as a product of the benzoyl peroxide reaction with iodine is formed together with the alkyl iodide but its yield diminishes with an increase in iodine concentration amounting to only 2 percent of the total iodine mixture at a 200 percent iodine excess.

Benzoyl peroxide reacts with perfluoroaliphatic carboxylic acids to yield perfluoroalkyl iodides in high yields. For instance, benzoyl peroxide and perfluorooctanoic acid reacted with iodine, 50 percent excess, in 1,3-dibromopropane solution to give a 60 percent yield of perfluoroheptyl iodide. The higher boiling 1,3-dibromopropane was used in place of 1,3- dichloropropane to effect easier separation of the product. Benzoyl peroxide, perfluoroaliphatic carboxylic acid and iodine (12221.5) reacted at C. for 2 hours in 1,3- dibromopropane solution (0.35 molar in benzoyl peroxide concentration).

The aromatic aroyl peroxides will react with aromatic acids in the presence of iodine to give a mixture of iodides, one corresponding to the acid and the other to the peroxide. This is illustrated for a 1:2 mole ratio of peroxide to acid in iodine (50 percent excess) solution of 1,3-dichloropropane as follows: (the figures in parenthesis are percent iodides formed based on the molar conversion of peroxide) benzoyl peroxide and mchlorobenzoic acid gave iodochlorobenzene (34 percent) and iodobenzene (38 percent); benzoyl peroxide and pnitrobenzoic acid gave iodonitrobenzene (13 percent) and iodobenzene (55 percent); p-nitrobenzoyl peroxide and benzoic acid gave iodonitrobenzene (16 percent) and iodobenzene (61 percent); benzoyl peroxide and anisic acid gave iodanisole (11 percent) and iodobenzene (32 percent); benzoyl peroxide and perfiuorobenzoic acid gave iodopentafluorobenzene 1.0 percent) and iodobenzene (21 percent).

Results of the reaction of BPIC and aliphatic and aromatic acids with iodine are shown in Table II. Higher product yields are obtained when the alcohols are distilled off as the reaction proceeds.

The preparation of heptadecyl iodide as now described is typical of the preparative procedures of this invention using an aroyl peroxide and BPIC.

BENZOYL PEROXIDE PROCEDURE Iodine (12.7 g., 0.05 moles), stearic acid (14.2 g., 0.05 moles), and benzoyl peroxide (6.05 g., 0.025 moles) were weighed into a flask equipped with a small distillation head. 1,3-Dichloropropane (42 ml.) and Freon 112 (25 mls.) were added as co-solvents, the latter to minimize the volume of the higher boiling dichloropropane and to fluidize the semi-dissolved mixture. A homogeneous solution was attained as the temperature was raised to the boiling point of the Freon which distilled with only small losses of iodine. When the temperature reached 1 10 C., heating was continued for a total time of 3 hours. All of the solvent and some of the benzoic acid was distilled from the mixture while the pressure was reduced and heating continued.

An ethereal solution of the residue was treated with sodium sulfite solution to remove free iodine and the solvent was the TABLE 1 Reaction of Benzoyl Peroxide and Octanoic Acid with iodine in 1,3-Dichloropropane evaporated. The crude product (20 g.) was eluted with 5 lzlPeroxide l-lodoheptane" lodobenzene" Consumed petroleum ether through a chromatographic column containing silica gel for separation of the bulk of heptadecyl iodide from residual benzoic acid. Evaporation of the main fraction 1.0 74 18 94 gave heptadecyl iodide (17.3 gr, Theory l8.3g.). Recrystal- 33 9 95 lization from a mixture of acetone (70 ml.) and 93 percent 10 90 7 100 ethanol ml.) at 40 yielded pure compound (13.0g., 71 percent yield). "yield based on peroxide TABLE II [Reaction of BPIC and aliphatic and aromatic acids with iodine] Molar ratio Reactants consumed Reaction conditions Iodide, Acid, I2, Perester, lime, Tempera Acid Acid I2 Parpercent percent percent percent hours ture, 0.

es er 2 1. 6 l 26 37 28 44 3 110 2 1. 5 1 16 15 68 99 2 120 2 1. 5 1 62 51 72 100 2 125 1 1 1 81 (B) 125 84 2 120-130 1 1 1 81 128 97 2 135 0. 5 1 1 82 140 93 2 115 Benzoic 1 1 1 72 100 94 2 11.5

B t-butylperony isopropyl carbonate.

Iodoheptane.

Alcohols not distilled ed as reaction proceeded. d Alcohols distilled oil as reaction proceeded. 8 Acid not experimentally determined.

1 1,3-diiodooctane. B Iodobenzene.

iodine (12.7 g., 0.08 M) and stearic acid (14.2 g., 0.05 M) were dissolved at 70 C. in 1,3-dichloropropane (45 mi.) in a round bottom flask (200 ml.) equipped with a nitrogen inlet and distillation head. BPlC (10.4 g. of 83 percent purity, 0.05 M) was added, the mixture heated at 125 C. for 1 hour to distill off the t-butanol and acetone formed. Reaction was completed at 135 C. for 2 hours after which the solvent (and some iodine) was distilled under an increased nitrogen flow. The crude product was dissolved in warm petroleum ether, some insoluble compound was filtered off and the solvent and iodine evaporated. Yield of crude produce was 16 g. (theory, 18.3 g.).

lclaim:

1. A process for preparing perfluoroalkyl iodides which comprises reacting a periluoroalkyl carboxylic acid with iodine and a peroxide selected from a group consisting of benzoyl peroxide, p,p-t-butylbenzoyl peroxide, toluoyl peroxide, chlorobenzoyl peroxide, nitrobenzoyl peroxide, and t-butylperoxyisopropyl carbonate in the presence of a solvent 

2. The process of claim 1 in which the acid is perfluorooctanoic acid and the peroxide is benzoyl peroxide. 